The present invention relates to a photometer. German printed patent application No. 29 10 188 and German printed patent application No. 15 98 893 disclose photometers wherein light beams traverse a measuring cuvette or chamber as well as a reference cuvette or chamber and are received by a gas filled detector or receiver having a cross section equaling the sum total of the cross section of measuring and reference cuvettes or chambers. Also, photometers are known wherein light beams having passed through measuring and reference chambers are received by solid state detectors whose radiation receiving surface is significantly smaller than the cross section of measuring and reference chambers. Such solid state receivers have the disadvantage therefore, that unless optical ray concentrating or focusing devices are included in the systems only a portion of the radiation that has passed through the various chambers are in fact detected. On the other hand such optical focusing equipment or the like can be quite expensive which is a cost increasing factor if the entire radiation area involved is rather large. This is particularly the case if thermo i.e. infrared radiation is involved. Moreover it may not always be possible to concentrate the entire amount of radiation involved by optical means upon the receiver. On the other hand the solid state detectors or infrared receivers have the advantage over gas filled detectors, that their stability lasts longer because they never run empty.
British Pat. No. 979,850 discloses a gas analyzer using two measuring chambers being passed through by infrared radiation. The radiation leaving the measuring reference chambers are detected under utilization of a semi-transparent mirror, which is arranged obliquely to the radiation in question. This analyzer presupposes for proper operation that a part of the infrared radiation reaching the detector traverses the oblique mirror and at the end of the chamber the radiation reaches a photoelectric cell after having passed through a filter, while another portion of the radiation reaching the detection chamber is reflected at right angles, passes through a second filter and is received by a laterally arranged photoelectric cell. The filters in this case have to be dimensioned so that the particular output characteristics of the photoelectric cells being connected in a differential circuit provide a characteristic value which is indicative of the concentration of the measuring gas contained in the measuring chamber. This analyzer therefore is different in principle from the type of analyzer to which the invention pertains. It is therefore a task to be solved by the invention to provide a photometer for fluid analysis using a solid state receiver which receives reference and measuring beams after having passed through appropriate gas chambers.
It is therefore an object of the present invention to provide a new and improved photometer in which measuring and reference beams are to be detected by a solid state detector.
In accordance with the preferred embodiment of the present invention it is suggested to provide the photometer in such manner that immediately behind the measuring and reference chambers a foil of polyvinyl-idene-fluoride is provided as a solid state receiver having a light responsive surface which is as large as a cross section through the measuring chamber or chambers. Alternatively, polyvinyl fluoride or polyvinylchloride can be used as solid state detector foil.
As far as the invention is concerned, matching of the dimensions, permits immediately the possibility of most favorable optical coupling. The foil made of polyvinyl idene fluoride PVDF may, to the extent it is round have a diameter from 14 to 25 mm. Quite analogously to a conventional photometer being equipped with a gas filled detector, now there is the advantage that focusing on other concentration of the impinging radiation is no longer necessary but of couse the solid state device suggested here avoids the drawbacks of the gas filled photometers as outlined above. Rather, the photometer constructed in accordance with the invention combines the advantages of an opto-pneumatic detector with the advantages of a solid state receiver, while avoiding disadvantages of either.
In accordance with a further development of the invention, the foil of the stated type can be arranged in a gas filled receiver chamber which absorbs infrared radiation, and, therefore, upon receiving radiation the chamber can be pyroelectrically as well as piezoelectrically effective, whereby the pyroelectric effect is used to determine reference signals while the piezoelectric effect is used to determine the measuring component. The piezoelectric effect results from the optopneumatic effect of the device in accordance with the invention, which also produces the pyroelectrical effect.
The measuring and reference signals will be separated by the device in accordance with the present invention under utilization of two specific features and characteristics of the specific solid state devices which features in fact become effective in sequence, whereby the utilization of the new photometer permits insitu application for measurement.
The detector itself is comprised of a chamber which is filled with the type of gas whose concentration is to be measured and determined or a particular representative substitute or replacement gas is used bearing as far as relevant absorption characteristics are concerned a well defined and therefore quantitatively ascertainable relationship to analogous qualities of the measuring gas.
One side of the measuring chamber is closed through a window that is transparent to infrared radiation, so that the radiation can indeed enter the chamber. Between the radiation source and the various devices all designed to absorb radiation to one extent or another, but upstream from the measuring chamber there is provided a modulation device which periodically interrupts the radiation at a particular, predetermined frequency. Moreover, a selection filter chamber may be provided in the radiation path, of a single path device, somewhere in front of the detector and being filled with a gas of the receiving kind which can be periodically inserted into and pulled out from the radiation path. The frequency of the motion of the filter chamber is smaller than the modulator frequency just referred to. The radiation passing into the filter chamber and absorbed therein will not be absorbed in any downstream absorption path, nor from the gas in the receiver and measuring chamber. Radiation permitted to pass the filter chamber will reach the device in accordance with the invention, in order to produce a pyroelectric effect whose intensity is proportional to the impinging radiation. This pyroelectric effect serves as a reference signal for the photometer.
Whenever the beam is not intercepted by the filtering chamber, all of the radiation includes also the absorption range in the gas in the receiver chamber. Therefore the receiver absorbs radiation otherwise filtered out occurs and is in effect converted into pressure causing some deflection of the foil. The degree and magnitude of that deflection depends on the preabsorption in the absorption path. And therefore can be used for the formation of a measuring signal, particularly under utilization of the piezoelectric effect of the foil.
The detector in accordance with the invention can be used in a photometer, wherein the radiation leaving the radiation source, but prior to reaching the detection chamber passes through an absorption chamber, being flown through on a continuous basis by measuring gas. Alternatively, the invention is useable in photometers for insitu measurements whereby the flow of gas to be analyzed passes generally between the radiation unit and the receiver unit.